"Create individual user" Route for internal API

[jeremy-london]

Our instance will not have team based competitions but will be individual members.

I want to be able to add a user programmatically through the internal API that mimics the "Add Users" section of the UI.

API would allow creation of new user with username/password and optionally assign to a team, if no team matches the requested team than auto-create the team

Additional context

Currently it looks like the only way to accomplish this is to script together the user/teams API and the user/accounts API to create a team with the user/teams API, then add a user with the user/accounts API.

[nickygerritsen]

Unlike the other import files, accounts.tsv is a bit strange: it is not directly linked to users:

• Besides containing the role, the first field also determines whether we need to create a team or link it to an existing team.
• If the role is team, the username field must be team-nnn with nnn a team number.

See https://ccs-specs.icpc.io/ccs_system_requirements#accountstsv for the format.
The other API endpoints do have JSON support based in the CCS specification API, and I have just created PR #942 that also allowd to add a single item directly instead of using a file.

My proposal is to create POST /api/users to create a new user, with our normal JSON structure, which then will add a user.
We can then also add GET /api/users and GET /api/users/<id>. All will only be allowed by admin's and omit passwords from the response.

Thoughts?

[jeremy-london]

Awesome idea! I think that would solve it well